The present invention relates to methods of assembling high-temperature electrochemical cells and is particularly directed to the problem of wetting cell components with molten salt electrolytes. Molten salt compositions including the alkali metal halides and alkaline earth metal halides do not readily wet various ceramic and metallic materials that are employed in various electrochemical cell components. Components such as interelectrode separators, particle retainers and current collectors are of particular concern.
The molten salt electrolyte is the medium for ionic conduction between electrodes and thus it must permeate into and wet the surfaces of the various materials within and between the electrodes. Particular problems in this regard have arisen with the various ceramic materials such as boron nitride, aluminum nitride, silicon nitride, zirconium dioxide, magnesium oxide, yttria and calcium zirconate. Separators are formed by fabricating these materials into woven fabrics, cloths, screens, felts, and compacts of fibrous and particulate materials. Materials such as boron nitride have been extremely difficult to wet with electrolytes that are mixtures of alkali metal chlorides such as LiCl-KCl.
Metallic components such as retaining screens and current collector structures include for instance, molybdenum, stainless steel, iron, iron-base alloys, nickel and nickel-base alloys. These materials, particularly when fabricated with abrupt sharp edges within their pores or mesh, are not readily wet with molten salt electrolytes.
Various prior methods for enhancing the wetting of components by molten electrolyte have included prewetting of individual components prior to cell assembly, filling electrolyte into assembled cells under vacuum conditions to draw the electrolyte into contact with porous and mesh members, cleaning and sand-blasting components to insure against surface impurities and an initial break-in exposure of the various components to molten salt within the cell structure. Although some of these methods have encountered some limited success, they are cumbersome and complicate the procedures for electrochemical cell initiation.